FM Bugger Circuit

                      FM Bugger Circuit

Here’s a great project from<a href="">EEWEb</a>.

Author : Charlene Tessa Descallar.

Editor : S. Sai Jayanth /LearntoDiscover.


The project circuit design is a FM Bugger circuit. It works like a the same frequency to be able to transmit and receive information in the same channel. The FM bugger circuit is originally designed to be used like a spy gadget to eavesdrop other people’s conversations. Though it is designed that way, it is pretty much useful as a transmitter or transmitter that transmits and projects information signals into the air wherein a FM radio will act as a receiver which would receive the transmitted signal. The circuit and the FM radio must be tuned-in with as a walkie-talkie to relay messages in a distance. {image3}


The FM bugger circuit is designed to be used as a spy gadget that would monitor a person through his conversations. Though it is illegal to be used in that way, there are actually spy agencies that would use bugger devices in spying someone. It is originally a spying device but it could also be used as a transmitter to transmit messages in a distance and receive the messages through a normal FM radio.

The operation of the FM bugger circuit is the same as of a transmitter. The audio or the information signal is the analog input of the circuit which will be picked-up by the mic. The input will be filtered by C1 which is used to remove the noise and distortions in the signal. The C6 and L1 serves as the tank circuit that will produce the carrier frequency for the input signal in which it will be modulated with a transistor. The modulated signal is then transmitted into the air through an antenna in sending it to a receiver with the same tuned-in frequency.
Figure 3  FM Bugger Circuit Diagram
The receiver for the FM bugger circuit can be just a normal FM radio. Both the transmitter and the receiver must be tuned-in with the same frequency to be able to transmit and receive information signals at the same channel. It can be done by adjusting the trimmer capacitor of the circuit to tune-in with the frequency channel of the FM radio or by adjusting the FM radio to tune-in with the frequency of the FM bugger circuit. When both are tuned-in with the same frequency channel, the FM bugger circuit is set to transmit messages and conversations from the line to another line which is the receiver.
Testing and Design Procedure

The FM bugger circuit is tested using <a href=””>Partsim</a> and the NGSpice to test the output of the circuit.
Figure 1 Circuit Simulation

FM Bugger Circuit Simulation
R1 Net1009 Mic 22K
R2 Net1009 Net1016 47K
R3 Net1003 0 33K
C1 Net1016 Mic 1NF
C2 Net1016 0 1NF
C3 Net1002 Net1003 4.7pF
C4 Net1002 Antenna 1NF
C5 Net1009 0 22NF
C6 Net1009 Net1002 50pF
L1 Net1009 Net1002 9NH
Q1 Net1002 Net1016 Net1003 2N2222
V1 Net1009 0 3V
V2 Mic 0 SINE ( 1 1 20Khz 0.0S )
R4 0 Antenna 1K
.options rshunt = 1.0e12 KEEPOPINFO
.MODEL 2N2222 NPN IS =3.0611E-14 NF =1.00124 BF =220 IKF=0.52 VAF=104 + ISE=7.5E-15 NE =1.41 NR =1.005 BR =4 IKR=0.24 VAR=28 ISC=1.06525E-11 NC =1.3728 RB =0.13 + RE =0.22 RC =0.12 CJC=9.12E-12 MJC=0.3508 VJC=0.4089 CJE=27.01E-12 TF =0.325E-9 TR =100E-9
·         OP Let expressions, if any:
write Net1002 Net1003 Net1009 Net1016 Mic Antenna I(V1) I(V2)
set appendwrite true
rusage everything
Figure 2 Output Signal Simulation

The simulation of the FM bugger circuit in PartSim shows that the circuit is working. The microphone was assumed to have an input of a 20 kHz sinusoidal wave. Then, the output signal at the load, R4 assumed to be the antenna for the circuit, turns out to produce a FM signal. Therefore, the FM bugger circuit itself has a great possibility to succeed and operate in real life when it will be put into test.

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